When does OSPF utilize a Link-State Update (LSU) message?

OSPF (Open Shortest Path First) utilizes Link-State Update (LSU) messages specifically to convey routing information and topology changes. When a router discovers a new link or a change in the network topology, it generates an LSU message to inform its OSPF neighbors about the current state of its interfaces and the routes associated with them. This allows all OSPF routers to maintain a synchronized view of the network topology.

The process begins with routers exchanging LSUs when they establish peering, which helps every router build its own Link-State Database (LSDB). Once the database is populated with LSAs (Link State Advertisements), routers can perform their shortest path calculations and create an updated routing table based on the latest topology information. Thus, LSUs play a crucial role in ensuring that OSPF can dynamically adapt to changes in the network, providing efficient and reliable routing.

The other options do not represent the primary function of LSU messages. For instance, the discovery of OSPF neighbors is primarily handled by Hello packets, and establishing new OSPF sessions involves different stages of neighbor formation. Sending OSPF process IDs is not a function related to LSUs but rather part of the overall OSPF configuration and operation.